Hao Li, and Hans-Martin Rein, “Millimeter-Wave VCOs With Wide Tuning Range and Low Phase Noise, Fully Integrated in a SiGe Bipolar Production Technology,” IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. 38(2), pp. 184-191, 2003 discloses an oscillator whose output comes from a load-connected collector in a differential Colpitts oscillator effective for low phase noise performance. C. Lee, T. Yao, A. Mangan, K. Yau, M. A. Copeland and S. P. Voinigescu, “SiGe BICMOS 65-GHz BPSK Transmitter and 30 to 122 GHz LC-Varactor VCOs with up to 21% Tuning Range,” IEEE CSIC Digest, pp. 179-182, 2004 discloses an oscillator using a cascode amplifier for output. Hao Li, Hans-Martin Rein, Thomas Suttorp, and Josef Bock, “Fully Integrated SiGe VCOs with Powerful Output Buffer for 77-GHz Automotive Radar Systems and Applications around 100 GHz,” IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. 39(10), pp. 1650-1658, 2004 discloses an oscillator having, at its rear stage, a driver amplifier for output.
In addition, an oscillator using a transformer for output has been introduced. For example, Japanese Patent Application Laid-Open Publication No. S54-32954 (1979) discloses a differential Colpitts oscillator using an MOS transistor, in which drain outputs are outputted through the transformer. Japanese Patent Application Laid-Open Publication No. H03-29504 (1991) discloses a differential cross couple oscillator using an inductor of a resonator as a transformer to take out an output. UK Patent Application Publication No. 2181913 A (1987) discloses a differential Colpitts oscillator provided with a transformer at its collector using a bipolar transistor.
In order to supply power more efficiently to a load having a predetermined impedance, the above “Millimeter-Wave VCOs With Wide Tuning Range and Low Phase Noise, Fully Integrated in a SiGe Bipolar Production Technology,” utilizes a load circuit provided to the collector for impedance matching, the above “SiGe BiCMOS 65-GHz BPSK Transmitter and 30 to 122 GHz LC-Varactor VCOs with up to 21% Tuning Range,” utilizes a load circuit of the cascode amplifier for impedance matching, and the above “Fully Integrated SiGe VCOs with Powerful Output Buffer for 77-GHz Automotive Radar Systems and Applications around 100 GHz,” utilizes a load circuit of the driver circuit for impedance matching. Meanwhile, each of Japanese Patent Application Laid-Open Publication Nos. S54-32954 and H03-29504, and UK Patent Application Publication No. 2181913 A realized impedance matching by adjusting the turn number of a transformer.